Supported chromium catalysts have long been a dominant factor in the production of high density olefin polymers such as polyethylene. As originally commercialized, these catalysts were used in solution polymerization processes. However, it early became evident that a more economical route to many commercial grades of olefin polymers was a slurry process, that is, a polymerization process carried out at a temperature low enough that the resulting polymer is largely insoluble in the diluent. However, certain control techniques which are easily carried out in solution polymerization systems become more difficult in the slurry system. This is particularly true with regard to control of molecular weight. In a solution system, the temperature can simply be increased in order to provide a lower molecular weight, higher melt flow polymer. However, in slurry systems, there is a practical limit on temperature increases, since the point is quickly reached wherein the polymer goes into solution and thus the value of the slurry system is lost.
In order to allow maximum utilization of the more commercially desirable slurry system, modifications of the catalyst system have been developed so as to allow the production of higher melt flow polymer. One such modification which has been utilized is to remove water from the silica at the hydrogel stage by means of azeotropic distillation or washing with a water miscible organic compound such as ethyl acetate. Of course, it is well known that there are many organic compounds which are miscible with water and thus capable of aiding in drying water from a substance.
It has been found, unfortunately, that some of the most desirable organic liquids for use in removing water from many standpoints turn out to be unacceptable when actually attempted on a commercial scale.